The subject invention relates generally to a fluid system with two hydraulic circuits having a common source of pressurized fluid and more particularly to a fluid system for the control of two hydraulic circuits that maintains priority to one of the circuits.
It is well known to provide a priority valve between a common source of pressurized fluid and the two separate circuits in order to provide priority to one of the circuits. However, in order to provide variable flow and pressure control to the other circuit while maintaining priority to the one circuit, added cost and complexity have been required. One example of such a system is set forth in U.S. Pat. No. 4,738,330 issued on Apr. 19, 1988 and assigned to Nippondenso Co., Ltd.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a fluid system is provided for two hydraulic circuits having a common source of pressurized fluid. The fluid system includes a reservoir operatively connected to the source of pressurized fluid, a source of power drivingly connected to the source of pressurized fluid, and first and second hydraulic circuits connected in parallel to the common source of pressurized fluid. The first hydraulic circuit is connected to the source of pressurized fluid and the reservoir. The first hydraulic circuit includes a first fluid actuator connected between the source of pressurized fluid and the reservoir, a first electrically controlled proportional relief valve connected between the source of pressurized fluid and the fluid actuator, and a second electrically controlled proportional relief valve connected between the reservoir and a point between the first electrically controlled proportional relief valve and the fluid actuator. The second hydraulic circuit is connected in parallel to the source of pressurized fluid. The second hydraulic circuit includes a second fluid actuator connected to the source of pressurized fluid and a control valve operatively disposed between the source of pressurized fluid and the fluid actuator.